The present invention relates generally to the field of semiconductor structures, and more particularly to the retention of strain and the control of germanium epitaxial growth thickness on FinFET device channels.
A pure semiconductor is a poor electrical conductor as a consequence of having just the right number of electrons to completely fill its valence bonds. Through various techniques (e.g. doping or gating), the semiconductor can be modified to have an excess of electrons (becoming an n-type semiconductor) or a deficiency of electrons (becoming a p-type semiconductor). In both cases, the semiconductor becomes much more conductive (the conductivity can be increased by one million-fold or more). Semiconductor devices exploit this effect to shape electrical current. The study of semiconductor materials is an important area of material science research due to their application in devices such as transistors and therefore computers.
The most commonly used semiconductor materials are crystalline inorganic materials, which are classified according to the periodic table groups of their constituent atoms and also whether they are composed of a single element or more than one element.
Field-effect transistors (FETs) are transistors that employ an electric field to control the conductivity of a channel in which one of the two types of charge carriers may travel. A FET is composed of a source and a drain connected by the channel through which the charge carriers, electrons or holes, pass when voltage is applied to a gate. The gate sits over the channel separated by an insulating material referred to as the gate dielectric. Applying voltage to the gate changes the amount of charge carriers in the channel thereby controlling the current in the device.
The term FinFET describes a non-planar, trigate transistor built on a silicon-on-insulator (SOI) or bulk silicon substrate. The distinguishing characteristic of the FinFET is that the conducting channel is a silicon or silicon germanium “fin”, which forms the body of the device. The wrap-around gate-over-fin channel structure provides better electrical control over the channel and thus helps in reducing the leakage current and overcoming other short-channel effects.
Charge carrier transport that is typically described by mobility through FET channels is an important factor for optimal performance. One way charge carrier transport can be modulated is through strain. For example, strained channels have been successfully integrated into Si- and Ge-based metal oxide semiconductor FETs (MOSFETs) to enhance carrier mobility.